Synthetic routes to functionalized polysiloxanes often suffer from complex methodologies, low yields, side reactions (e.g. involving rearrangements and/or degradation), or minimal characterization of the product(s). It generally known to synthesize alkoxysilanes under mild and neutral reaction conditions using metal-catalyzed oxidation reactions of monomeric hydrosilanes. The reported methods can suffer from the disadvantage of the non-selective modification of Sixe2x80x94H bonds, which leads to susceptibility of the Sixe2x80x94H bonds toward side reactions including dehydrocoupling, rearrangement and/or backbone degradation reactions. The formation of mixtures of xcex1 and xcex2-isomers, insoluble materials and rearrangement products are common drawbacks of reported methods.
Accordingly, it would be advantageous to provide a method of preparing a poly((aminofunctional alkoxy)-alkylsiloxane) using a relatively simple method under relatively mild reaction conditions. It would also be advantageous to provide a method of preparing a poly((aminofunctional alkoxy)-alkylsiloxane) that allowed for the selective alcoholysis of Sixe2x80x94H bonds without significant degradation of the siloxane backbone. It would also be advantageous to provide a method of preparing a poly((aminofunctional alkoxy)-alkylsiloxane) that allowed for monitoring of the reaction progress (e.g. by NMR). It would also be advantageous to provide a poly((aminofunctional alkoxy)-alkylsiloxane) product in a relatively high yield. It would be desirable to provide a method of preparing a poly((aminofunctional alkoxy)-alkylsiloxane) having one or more of these or other advantageous features.
The present invention relates to a method of preparing aminofunctional polysiloxanes. More particularly, the present invention relates to a method of preparing aminofunctional alkoxy polysiloxanes. The method includes reacting a polyhydrosiloxane with an alcohol reactant including an aminoalcohol to form the aminofunctional alkoxy polysiloxane. The reaction is typically carried out in the presence of a catalyst, e.g., a dehydrogenative coupling catalyst which includes a rhodium compound.
The present application also provides a coating composition which includes an aminofunctional alkoxy polysiloxane. The coating composition is particularly suitable as an adhesive or primer for coupling a topcoat to a substrate. The aminofunctional alkoxy polysiloxane may serve as the primary resin in the coating composition or in other embodiments, an aminofunctional alkoxy polysiloxane may act as a crosslinking agent and/or curing accelerator, e.g., in epoxy-based coating compositions.
The present aminofunctional alkoxy polysiloxane compound can be a linear and/or cyclic alkoxy polysiloxane. As used herein, the term xe2x80x9caminofunctional alkoxy polysiloxane compoundxe2x80x9d refers to an alkoxy substituted polysiloxane compound which includes one or more aminofunctional alkoxy groups. For the purposes of this application, the term aminofunctional alkoxy group refers to groups which include at least one basic nitrogen atom and encompasses groups resulting from the removal of a hydroxyl hydrogen atom from an amino functional alkanol (e.g., xe2x80x94Oxe2x80x94CH2CH2xe2x80x94Oxe2x80x94CH2CH2NH2), an amino functional cycloalkanol, and/or an amino functional hydroxy-substituted aryl compound (e.g., xe2x80x94Oxe2x80x94C6H4xe2x80x94Oxe2x80x94CH2CH2NH2). As employed herein, the term xe2x80x9carylxe2x80x9d refers to both hydrocarbon aromatic groups and heteroatom-containing aromatic groups. For example, the aminofunctional alkoxy group may be an aminofunctional pyridyloxy group (i.e., a group resulting from the removal of the hydroxyl hydrogen atom from an aminofunctional hydroxypyridine).
Amino groups are organic functional groups which contain a basic nitrogen atom. Examples of amino groups include aliphatic amino groups, such as mono-, di- and trialkylamino groups; cycloaliphatic amino groups, such a piperidinyl and piperazinyl groups; aromatic amino groups (i.e, where the basic nitrogen atom is part of an aromatic ring), such as pyridyl groups, pyrimidyl groups and pyrazinyl groups; and amino-substituted aromatic groups (i.e., where the basic nitrogen atom is directly bonded to an aromatic group), such as aminophenyl groups (e.g., xe2x80x94NHxe2x80x94C6H4 and xe2x80x94C6H4xe2x80x94NR2) and aminopyridyl groups.
As employed herein, the term xe2x80x9calkoxy groupxe2x80x9d encompasses functional groups which include an alkyl-OH, cycloalkyl-OH or aryl-OH functional group whether or not the overall group includes an amino functional group, i.e., an aminofunctional alkoxy groups constitute one type of alkoxy group but not all alkoxy groups necessarily include a basic nitrogen atom.
As illustrated in formula (I) below, the siloxane subunits may not all contain an aminofunctional alkoxy group. Typically, at least a majority and, in many instances, all of the siloxane subunits of the polymer include an aminofunctional alkoxy group. Polysiloxanes where not all of the siloxane subunits of the include the same substituents polymer (with the exception of the terminal subunits) are referred to herein as xe2x80x9cpolysiloxane copolymers.xe2x80x9d As used herein, such xe2x80x9ccopolymersxe2x80x9d can have two or more different siloxane subunits. Polysiloxane copolymers can be formed by reacting a mixture of two alcohols, e.g., a mixture of 2-aminoethanol and ethanol, with a polyhydrosiloxane. Generally, the different siloxane subunits are randomly distributed in a polysiloxane copolymer (a xe2x80x9crandom copolymerxe2x80x9d). However, by using appropriate synthetic methods known to those of skill in the art, polysiloxane copolymers in which the different siloxane subunits are present in xe2x80x9cblocksxe2x80x9d of two or more identical adjacent subunits can also be produced (xe2x80x9cblock copolymersxe2x80x9d). The present polysiloxane copolymers typically have a ratio of siloxane subunits containing an aminofunctional alkoxy group to subunits which do not include an aminofunctional alkoxy group of about 20:1 to 1:20.
Throughout this disclosure, the text refers to various embodiments of the aminofunctional alkoxy polysiloxane compounds and methods of preparing and using the compounds. The various embodiments described are meant to provide illustrative examples and should not necessarily be construed as descriptions of alternative species. Rather it should be noted that the descriptions of various embodiments provided in this disclosure may be of overlapping scope. The embodiments discussed in this disclosure are merely illustrative and are not meant to limit the scope of the present invention.